ARTHROPODA 265 
(ii.) The Eucopepoda are further subdivided into: (a) the 
Gnathostomata or free-swimming forms with masticating mouth 
appendages; and (b) the Parasitica, in which the mouth parts 
are modified for sucking or piercing, and whose body ws imeom- 
pletely segmented. 
(a) GNATHOSTOMATA.—The genus Cyclops, which includes 
many species living in fresh or brackish water in Great Britain, 
is fairly typical of this subdivision. In shape its body has been 
compared to that of a split pear with its flat side ventral, 
tapering posteriorly. The head bears five pairs of appendages, 
viz. (i.) antennules, (ii.) antennae, (iii.) mandibles, (iv.) Ist 
maxillae, (v.) 2nd maxillae. Dorsally its terga form a con- 
tinuous carapace, and are fused with the first thoracic tergum. 
The thorax consists of six segments, the five posterior being 
free dorsally as well as ventrally, except in the female, where 
the last thoracic segment is fused with the first abdominal. 
The abdomen consists of four cylindrical segments devoid of 
appendages, the last bears the furcal caudal processes so 
characteristic of the Entomostraca. 
Appendages of Cyclops. 
1. Antennules. 5. 2nd maxillae (maxillipedes). 
2, Antennae. 6-9. Four pairs of thoracic limbs. 
3. Mandibles. 10. 5th pair sp rr 
4, Ist maxillae. (rudimentary). 
The antennule is a well-developed appendage, which acts 
as a strong oar, in the male it also acts as a clasper, and 
is correspondingly modified; the antennae are short and 
four-jointed ; the mandibles guard the mouth, one on each 
side; they and the 1st maxillae have rudimentary palps. 
The 2nd maxillae are biramous, the split extending to their 
base; the shell gland or excretory organ opens upon the 
first joint of the outer ramus. The first four thoracic limbs 
are flattened from before backward; they are biramous, and 
their bases are united by a median plate, which extends across 
the middle ventral line. The fifth thoracic segment bears a 
pair of rudimentary feet at the sides of the ventral surface. 
The next segment has a rounded cross section like those of the 
abdomen, with which it is generally grouped; but as it bears 
the openings of the genital ducts, it is better to regard it as 
